This is a list of ontologies that are fully documented, dereferenceable, used by independent data providers and possibly supported by existing tools. In order to be in this list, the ontology must have a documentation page which describes the ontology itself, as well as all the terms defined by the ontology. It must also be used by 2 (verifiable) independent datasets (not coming from the same provider nor interdependent providers).
The Dublin Core (DC) ontology
Project homepage: http://dublincore.org/
Typical prefix: dc: and dcterm:
Description: this is a light weight RDFS vocabulary for describing generic metadata.
Which datasets use it: DC is ubiquitous in the Linked Data landscape.
Tools supporting it: the Protégé ontology editor provides DC properties as default annotation properties for ontologies and ontological terms. Providing DC annotations is also very common in other Semantic Web editors.
Technicalities: DC is a moderately small ontology divided into 2 vocabularies: DC elements and DC terms. DC elements contain 15 properties. DC terms contain 22 classes and 55 properties. It is not an OWL 2 DL ontology because it does not rely at all on the OWL constructs. This actually makes it a very simple ontology to reason with. Since the terms are weakly constrained, it is often the case that ontologies reusing them are redefining the terms internally instead of importing the DC ontology. This way, it is possible to choose, e.g., whether the properties are AnnotationProperties, etc. without breaking the compatibility with, for instance OWL DL.
The Friend Of A Friend (FOAF) ontology
Project homepage: http://www.foaf-project.org/
Typical prefix: foaf:
Description: this ontology is used to describe people and social relationship on the Web. It is mostly focused on people's existence in the virtual world, with many properties related to online activity or identity: foaf:mbox, foaf:skypeID, foaf:msnID, foaf:geekcode, etc. Nothing about family relations, physical address... It provides similar information on organisations or groups with a similar focus on their existence on the Web (work place webpage, etc). It is particularly well suited for describing people on Web-based Social platforms (facebook, twitter, blogspot, ...).
Which datasets use it: FOAF is used on many different websites. The list would be too long for this page. Notable examples are: Live Journal, etc. Many computer scentists in the Semantic Web field all over the world are publishing their personal FOAF file.
Tools supporting it: FOAF-a-Matic is a Web-based app which allows the user to create a FOAF file quickly by entering natural language text information in a Web form. The Wiki of the FOAF project has a webpage listing many FOAF-related tools.
Technicalities: FOAF is a rather small ontology (19 classes, 44 object properties, 27 datatype properties). It is not an OWL 2 DL ontology because it relies on inverse functional datatype properties. However, apart from this small issue and minor syntactical issues, the ontology is essentially compatible with OWL 2 RL, which means it is particularly suitable for materialising implicit knowledge about FOAF data in a triple store.
Socially Interconnected Online Communities (SIOC) ontology
Project homepage: http://sioc-project.org/
Typical prefix: sioc:
Description: this ontology is used to describe online communities such as forums, blogs, mailing lists, wikis. It complements FOAF by stressing on the description of the products of those communities (posts, replies, threads, etc).
Which datasets use it: SIOC is used on many different websites. Notable examples are: ???.
Tools supporting it: most notably, Wordpress and Drupal have a module supporting it. There is a page that references many applications using SIOC.
Technicalities: SIOC is a lightweight ontology (17 classes, 61 object properties, 25 datatype properties). It is essentially in OWL 2 DL, with tiny syntactical issues that strictly speaking makes it a non DL ontology. It only relies on OWL 2 RL constructs.
Project homepage: http://purl.org/goodrelations/
Typical prefix: gr:
Description: this ontology is used to describe products sold online. It is especially useful to online stores with a great diversity of products.
Which datasets use it: BestBuy.com announced that they are publishing RDF descriptions of their products, using Good Relation ontology. See also a list of examples in the wild.
Tools supporting it: List of applications.
Technicalities: Good Relations is a moderately small ontology (27 classes, 43 object properties, 37 datatype properties and 43 individuals). It is a perfectly valid OWL DL ontology. It is fairly expressive, such that it is not in any of the 3 OWL 2 profiles.
The Music Ontology
Project homepage: http://musicontology.com/ (it's just the spec page)
Typical prefix: mo: or music:
Description: this ontology is used to describe information related to the music industry. It does not provide any means to describe in detail the music itself (notes, instruments, rythms, etc) but focus more on releases, live events, albums, artists, tracks that characterise most of the business-related information about music that can be found on the Web.
Which datasets use it: the BBC is using it to describe its musical programmes. What else?
Tools supporting it: DBtune, and?
Technicalities: The Music Ontology is a moderately large ontology, which imports 3 external ontologies, which in turn import 2 additional ones. In total, the import closure defines 141 classes, 260 object properties, 131 datatype properties and 86 individuals. The atomic ontology itself defines ... It is not properly speaking an OWL DL ontology due to small syntactic problems, but it essentially relies on DL constructs. It is fairly expressive, such that it cannot be treated as part of any of the sublanguages of OWL 2 DL.
Project homepage: http://www.ics.forth.gr/isl/MarineTLO/
Typical prefix: marineTLO:
Description: MarineTLO is a top-level ontology for the marine domain (also applicable to the terrestrial domain).
Which datasets use it: FP7 iMarine Project is using it as an unified and coherent core model for schema mapping among different sources which enables formulating and answering queries which cannot be answered by any individual source.
Tools supporting it: MarineTLO-based Warehouse. It is a warehouse which integrates information coming from FishBase, WoRMS, ECOSCOPE, FLOD and DBpedia. It currently contains information (≈ 3M triples) about marine species (≈ 40,000), ecosystems, water areas, vessels, etc. The warehouse is already in use by various services offered by iMarine and it keeps evolving. (SPARQL endpoint, browsing interface restricted access, Please contact for credentials)
Technicalities: MarineTLO ontology is an ongoing activity and the last version (http://www.ics.forth.gr/isl/MarineTLO/#releases) contains 92 classes and 41 properties. It is represented in OWL 2.